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United States Department of Agriculture

Agricultural Research Service

Title: Mid-Infrared Versus Near-Infrared Diffuse Reflectance Spectroscopy for Quantitative and Qualitative Analysis of Agricultural Products

Authors
item Reeves Iii, James
item Zapf, C - MCCORMICK CO, INC
item Delwiche, Stephen
item Simkovic, I - SLOVAK ACADEMY OF SCIENCE

Submitted to: Research Signpost: Research Developments in Agricultural and Food Chemistry
Publication Type: Review Article
Publication Acceptance Date: August 1, 1999
Publication Date: N/A

Interpretive Summary: Spectroscopy uses the interaction of light to study or determine the composition of materials. Over the last 20 years or so, light just beyond the range of human sight called near-infrared (NIR) has been used extensively to determine the composition of agricultural products. Beyond the NIR lies the mid-infrared (MIDIR), also invisible to humans, and more commonly known as radiant heat. While MIDIR spectroscopy has been extensively used in the scientific community for various functions, it has only recently been explored for uses common to the NIR. Studies were conducted to determine the advantages and disadvantages of the two for the study of agricultural products. In studies comparing the two for the analysis of agricultural products, it has been shown that MIDIR spectroscopy can be used for many of the same purposes for which near- infrared spectroscopy (NIRS) has come to be so extensively. It has also been shown that in some cases results based on MIDIR spectra appear to offer some advantages as compared to NIR spectra, but that, as yet, no case has been found where the MIDIR was an obvious choice, and questions still remain as to the relative robustness of calibrations based on MIDIR spectra as compared to NIR spectra (how well the relationships between spectra and composition stand the test of time). It needs to be understood, however, that for most agricultural applications, MIDIR spectroscopy is in a much more primitive state of development than NIRS. In conclusion, work has demonstrated that MIDIR spectroscopy may have benefits for determining the composition of agricultural materials, but more research is needed to determine its true potential relative to NIRS which is extensively used today.

Technical Abstract: In studies comparing mid- and near-infrared reflectance spectroscopy for the quantitative and qualitative analysis of agricultural products, it has been shown that mid-infrared (MIDIR) spectroscopy can be used for many of the same purposes for which near-infrared spectroscopy (NIRS) has come to be so extensively used over the last two decades. It has also been shown that in some cases results based on MIDIR spectra appear to offer some increase in accuracy as compared to near-infrared (NIR) spectra, but that, as yet, no case has been found where the MIDIR was an obvious choice based on an increased calibration accuracy alone (quantitative or qualitative), and questions still remain as to the relative robustness of calibrations based on MIDIR spectra as compared to NIR spectra. It needs to be understood, however, that with regard to the type of applications examined here, MIDIR spectroscopy is in a much more primitive state of development than NIRS. Decades of work have gone into optimizing NIR spectrometers and sampling devices for their intended uses. While the same can be said for the MIDIR spectrometers, the intended uses were not the same. Thus, rotating sample cups and cells for large or unground samples do not commercially exist. Even simple questions like, what spectral resolution is needed for a given task, have barely been explored. In conclusion, work has demonstrated that MIDIR spectroscopy may have many benefits for determining the composition of materials of interest to the agricultural and food communities, but more research is needed to determine its true potential relative to NIRS which is extensively used today.

Last Modified: 10/24/2014